Hexafluoroacetone is produced in a large amount as an industrial raw material of 2,2-bis(4-hydroxyphenyl)hexafluoropropane (bisphenol-AF), which is important as a crosslinking agent of fluororubber, hexafluoroisopropanol, which is important as a medicine intermediate, and the like. Industrially, hexafluoroacetone is produced by a process by an epoxidation of hexafluoropropene and a subsequent isomerization, a process by subjecting hexachloroacetone obtained by chlorinating acetone to a substitution fluorination with hydrogen fluoride by a chromium-supported activated carbon catalyst or the like, etc. Hexafluoroacetone is a gas having a boiling point of −28° C. under atmospheric pressure. Therefore, in order to meet the convenience of handling, hexafluoroacetone trihydrate, which is obtained as a constant boiling composition of 106° C., is used as a raw material in many reactions or served for storage. There are, however, some cases in which existence of water is not permissible depending on the reaction conditions, the target product and other requirements. Furthermore, hydrates are generally lower in reactivity in many cases, as compared with anhydrides. Therefore, anhydride of hexafluoroacetone is requested in some cases, and upon use it is frequently conducted to convert the hydrate to the anhydride in place.
As a process for dehydrating a hexafluoroacetone hydrate, there have been reported processes by the contact with Molecular Sieve (a registered trade mark) (Patent Publication 1), concentrated sulfuric acid, sulfuric anhydride, phosphorus pentoxide (Patent Publication 2), etc. By using concentrated sulfuric acid, sulfuric anhydride, phosphorus pentoxide, fuming sulfuric acid or the like as the dehydrator, hexafluoroacetone decomposition products may be produced. Furthermore, there occurs a waste in a large amount of sulfuric acid or phosphoric acid containing water and organic matters produced by the decomposition. Furthermore, there is also a problem that recovery percentage of hexafluoroacetone is not necessarily high when the dehydration is conducted by these processes including the case of using a synthetic zeolite.
On the other hand, hydrogen fluoride may be used as a catalyst or solvent in reactions using hexafluoroacetone as a raw material. For example, bisphenol-AF is obtained by a dehydration reaction from a mixture of hexafluoroacetone, phenol and hydrogen fluoride (Non-patent Publication 1).    Patent Publication 1: Japanese Patent Application Publication 59-157045    Patent Publication 2: Japanese Patent Application Publication 57-81433    Non-patent Publication 1: Isz. Akad-Nauk SSSR, Otdel. Khim, Nauk, vol. 4 pp. 686-692 (1960); English version pp. 647-653